According to the conventional method of controlling the molecular weight distribution of high 1,4-cis polybutadiene (hereinafter referred to as "high-cis BR"), a method of using organonickel compound, organoaluminum compound and fluorine containing compound as a main catalyst, together with halogen-substituted phenol derivatives as an additive, was disclosed in the U.S. Pat. No. 5,100,982.
The U.S. Pat. No. 5,451,646 also disclosed a method of using organonickel compound, organoaluminum compound and fluorine containing compound as a main catalyst, together with p-styrenated diphenyl amine to control the molecular weight of the high-cis BR, thereby improving the processability.
Further, the Japanese Patent No. 78-51,286 disclosed a method of preparing the high-cis BR with a narrow range of molecular weight distribution using nickel compound, boron compound, alkyllithium and alkylbenzene sulfonate.
In addition, the U.S. Pat. No. 4,533,711 disclosed a method of further extending the molecular weight distribution, wherein rare earth metal compound belonging to the atomic number of 57 to 71, organoaluminum compound and halogenated aluminum compound were employed as a main catalyst, while using organoaluminum hydrides or hydrocarbons compounds containing activated hydrogen as an additive.
However, the conventional methods of controlling the molecular weight distribution in preparing the high-cis BR have affected the main physical properties of polymer such as solution viscosity and Mooney viscosity, thus resulting in increasing cold-flow.